Conventionally, on optical semiconductor devices used for communications, a semiconductor laser as light source and a lens system are mounted, and an optical fiber is introduced from outside, for connection. Then, laser light modulated by a signal is rendered parallel by a collimator lens system or converged by a lens (system) for convergence, for outputting into the optical fiber.
Generally, the former uses two collimator lenses and is used for applications in which high precision in terms of the optical coupling is required, and the manufacturing cost of the former tends to be higher. For example, structures as described in Patent Documents 1 and 2 are known. The latter uses one lens for convergence, and is used for applications in which comparatively low precision in terms of the optical coupling suffices. The manufacturing cost of the latter can be low.
On the other hand, depending on whether the optical fiber connected to the optical semiconductor device is a multi-mode optical fiber which supports propagation of a plurality of modes or a single-mode optical fiber which supports propagation of only one mode, the precision of the optical coupling required for the optical semiconductor device differs. Generally, the higher precision of optical coupling is required in the optical semiconductor device connected to the single-mode optical fiber. Thus, this optical semiconductor device has higher performance, but its manufacturing cost tends to be higher.
[Patent Document 1]
Japanese Patent Kokai Publication No. JP-A-4-320079
[Patent Document 2]
Japanese Patent Kokai Publication No. JP-A-8-146352